Flame retardant compositions

ABSTRACT

Novel tin containing flame retardants for synthetic polymers that exhibit reduced tin content simultaneously with effective flame retarding characteristics consist of one part by weight of hydrated stannic oxide in combination wtih four parts of a member selected from the group consisting of colemanite (calcium borate hexahydrate), zinc oxide and mixtures of zinc oxide and magnesium oxide. Polymer compositions containing these flame retardants possess improved flame retarding characteristics simultaneously with effective color stability in the presence of heat and at a substantial reduction in cost over polymers containing known flame retarding compositions.

Uited States Patent [1 1 Touval Dec. 16, 1975 FLAME RETARDANT COMPOSITIONS [75] Inventor: Irving Touval, Edison, NJ.

[73] Assignee: M&T Chemicals Inc., Greenwich,

Conn.

[22] Filed: Sept. 11, I974 [21] Appl. No.: 504,863

Related US. Application Data [63] Continuation-in-part of Ser. No. 68,538, Aug. 31,

1970, abandoned.

[52] US. Cl... 260/28.5 A; 260/28.5 B; 260/28.5 D; 260/45.7 P; 260/45.7 R; 260/45.75 W;

260/45.75 D; 260/45.85 V; 260/45.95 G

[51] Int. Cl. C08K 3/20; C08K 3/24; CO8K 5/02 [58] Field of Search ..260/45.75 W, 45.75 D, 260/45.7 R, 45.7 P, 45.95 G, 4585 V-,

260/28.5 B, 28.5 D, 28.5 A

[56] References Cited UNITED STATES PATENTS 1,990,292 2/1935 Leatherman 260/45.75 2,286,744 6/1942 Leatherman... 260/45.75

2,610,920 9/1952 Hopkinson 260/45.75 3,202,567 8/1965 Muri et al. 260/45.75 3,524,761 8/1970 Humphrey 260/45.75

FOREIGN PATENTS OR APPLICATIQNS 1,080,468 8/1967 United Kingdom OTHER PUBLICATIONS The Chemistry and Uses of Fire Retardants- Lyons; 1970; pp. 80-88, 221 and 222.

Combustion and Flame-l4, pp. 135 to 139; 1966; article by Fenimore.

Primary Examiner-V. P. Hoke Attorney, Agent, or FirmRobert P. Auber; Kenneth G. Wheeless; Robert Spector [57] ABSTRACT 9 Claims, No Drawings FLAME RETARDANT COMPOSITIONS BACKGROUND This application is a continuation-in-part of application, Ser. No. 68,538, filed Aug. 31, l970 now abandoned.

This invention relates to novel flame retardant polymer compositions. More particularly, this invention relates to tin-containing flame retardants with significantly less tin than required in prior art formulations to provide an effective level of flame retardancy for synthetic polymers.

With the increasing use of synthetic polymers, as in the construction industry, for example, the level of flame retardancy exhibited by these materials have become increasingly important. Many efforts have therefore been made to develop flame retardant additives for synthetic polymers which will improved flame retardancy without imparting undesirable properties to the final resin composition, such as, for example, interference with a desired color, and even more importantly affecting the tensile properties of the polymer being used so as to decrease its effectiveness for a given end use. An equally important consideration is the cost of a flame retarding additive, particularly in large scale operations involving processing literally thousands of pounds of polymer.

Various antimony compounds, particularly oxides, effectively flame retard polymer compositions when used in combination with an organic halogen source. These flame retardants do not adversely affect the stability of polymer compositions in the environments encountered during their processing and use. However, antimony compounds have recently become relatively scarce and expensive. The use of antimony-containing DETAILED DESCRIPTION oETI-IE INVENTION The present flame retardants contain one part by weight of hydrated stannic oxide and four parts of colemanite, zinc oxide, or mixtures of zinc oxide with magnesium oxide. The magnesium oxide is particularly useful in combination with zinc oxide for imparting heat stability to homopolymers and copolymers of vinyl chloride.

Acceptable levels of flame retardancy are obtained for all of the aforementioned synthetic polymers by replacing on an equal weight basis the conventional antimony compounds such as antimony oxide, with the present flame retardants. Specifically, the flame retardants are usually employed at concentrations of between about 05-25 phr (parts per hundred parts compounds for flame retarding may therefore not be economically feasible for some large scale processes.

Various substituted for antimony compounds have been proposed, including zinc compounds, certain hydrated borates, barium oxide, hydrated tin oxide and combinations of these compounds. While many "of these substitutes are lower in cost relative to antimony compounds, they have not proven to be equivalent to antimony compounds with regard to flame retardancy. Some substitutes which are equivalent in performance interfere with the mechanical and/or esthetic characteristics of the polymer composition. Of the various proposed substitutes, tincompounds have proved most effective. However, certain tin compounds, such as hydrated tannic oxide, for example, are almost as expensive as antimony thus eliminating any economic advantage for a weight-for-weight substitution of a tin compound for a antimony compound.

An objective of this invention is to provide tin-containing flame retardants that offer performance equivalent to that of antimony compounds at a lower cost.

SUMMARY OF THE INVENTION resin). A preferred range is determined by the particular polymer substrate being flame retarded. For example,'if the polymer is polyvinyl chloride, or other chlorine-containing polyolefin, the concentration range is 05-10 phr. For non-halogenated polymers such as polyethylene and acrylonitrile-butadiene-styrene terpolymers, the preferred range of flame retardant concentration is between 4 and 25 phr. Polyurethanes require a lower concentration, usually between 4-14 phr, preferably about 10 phr of the flame retarding agent.

Hydrated stannic oxide imparts acceptable levels of flame retardancy to cellusloic materials, particularly fabrics, as disclosed in U.S. Pat. No. 1,990,292. However, the oxide is virtually ineffective as a flame retardant for synthetic polymers in the absence of an organic compound which functions as a source of halogen at flame temperatures. The halogen can be chlorine, bromine or iodine. The concentration of halogen source is equivalent to between one and about twelve times the weight of the present flame retarding agents. If the polymer being flame retarded contains a sufficient amount of halogen, i.e. about 20 percent by weight or more, no additional halogen source is required. Polyvinyl chloride contains 57 percent by weight of chlorine, and can therefore function as a halogen source.

In the event that an organic halogen source other than the substrate polymer is required, one can employ any organic halogen-containing compound that is not so volatile or heat sensitive as to boil or decompose below 300C. Suitable organic halogen sources contain between 2 and 20 carbon atoms. Since halogenated hydrocarbons are usually the least expensive halogen sources, this class of compounds is preferred, although other classes of halogen-containing organic compounds such as alcohols, acids, esters, ketones and amines are also suitable. The hydrocarbon portion of the molecule can be aliphatic, cycloaliphatic or aromatic. Specific examples of preferred halogen sources include chlorinated paraffin waxes and compounds containing two or three fused carbocyclic rings, as represented by the formula The following table lists some of the representative compounds from the various classes of halogen sources and the types of polymer substrates most suitable for use with these compounds.

CHLORINATED COMPOUNDS Alkanes Chloroethanes Chlorop ropanes Chlorinated fish oil Chlorinated rubber Chlorinated PVC Chlorinated polyisobutylene Chlorinated polyolefins Polyvinyl chloride Benzene heXachIoride-C H CL, Olefins Chloroethylenes, vinyl chloride Chloropropene Chlorobutene and butadiene Chloroprene Vinyl chloroacetate Allyl chloride Hexachlorocyclopentadiene and derivatives (hex") Chlorendic acid and derivatives USE Paint, polystyrene Polyesters Paints, wood, textiles. polyolefins Paint Rubber Vinyls, textiles Polyurethane Polyolefins Textiles Cellulose derivatives Textiles, polystyrene. acrylics Polystyrene. vinyls, acrylics Rubber, vinyls Polyolefins Polyesters, acrylics Epoxies Paints, polyesters, polyurethanes, epoxies, polystyrene, acrylics Polyesters. polyurethanes, epoxies, vinyls Alcohols, acids, aldehydes and other functional compounds Chloroalkyl acrylonitrile Chlorinated aryldiamines Aromatics Alkoxychlorobenzenes Chlorinated hexamethylbenzene Chlorinated alkylaryl ethers Chlorophenols Pentachlorophenol glycidyl ether Chlorostyrenes Chlorothiophenol esters Chlorinated l,4-bis-hydroxymethyl benzene Chlorophenyl isocyanate Chlorobiphenyls and polyphenyls Chlorinated 4,4'-bis-hydroxybiphenyl Chlorinated 3,3'-bis-isocyanatobiphenyl Chlorinated naphthalenes Chlorinated bisphenol A and glycidyl ethers Chlorinated diphenyl carbonate Tetrachlorophthalic acid and derivatives Chlorinated alkyd resins Cl Cl Chloranil Cl Cl Alkanes I Bromoethanes Bromocycloalkanes Vinyls, polyesters Polyesters, polyurethane Epoxies Epoxies Polyesters, polyurethane Nylon, vinyls Polyesters Polyurethane Polystyrene Polyurethane, epoxies. polyaldehydes Acrylics Epoxies Vinyls Vinyls Polyesters Textiles, styrene, acrylics, wood phenolics, polyphenylenes Polyurethane epoxies Polyesters, polystyrene, polyolefins Acrylics, vinyls Cellulosics, textiles Textiles Textiles, polyesters. polyurethane. polystyrene Polyesters Polyurethanes Textiles, polyesters Polyesters, epoxies Polycarbonates Textiles. polyesters Paints Vinyls Vinyl Polymers Polyolefins -continued CHLORINATED COMPOUNDS USE Bromocycloalkanol, acrylic acid ester Brominated polybutadiene Olefins Acrylic Polymers Vinyl and styrene polymers Vinyl bromide Polystyrene, acrylics Tetrabromododecene Polyesters Hexabromobicycloheptene derivatives Brominated cyclododecatriene Hexabromo cyclopentadiene Acrylics Alcohols, acids, aldehydes and other functional groups 2,3,3-Tribromoallyl alcohol Polystyrene,vinyls and esters (e.g., acrylate esters) 2,2,3,3-Tetrabromobutanel ,4diol Polystyrene Brominated pentaeythritol Polyesters Brominated polyols Polyurethanes 2,3-Dibromopropyl phthalate Paper Brominated tall oil Polyurethanes 2,2-Bis( bromomethyl l ,3- Polyesters propanediol 2-Bromoethyl itaconate Dibromosuccinic acid Bromoacetaldehyde, bromobenzaldehyde Brominated amides BrCH R Polystyrene, acrylics Polyesters Polyvinyl alcohol anhydride Bromophthalimide Tetrabrornobisphenol A Nylon type polymers Epoxies Brominated salicylanilide Hydrated stannic oxide exhibits the general formula SnO .0.52H O. This compound is a more effective synergist than the anhydrous oxide when used in combination with colemanite or zinc oxide. This is surprising considering the fact that the anhydrous oxide has the higher tin content of the two (77 percent by weight of tin for the anhydrous oxide, compared with between 62 and 67 percent for the hydrated form).

Hydrated stannic oxide can be prepared by reacting stannic chloride with an aqueous solution of a basic salt such as sodium carbonate. The resultant precipitate is isolated and dried to obtain hydrated stannic oxide of the desired particle size. Since dehydration of the oxide to the anhydrous form occurs at a temperature above about 400C., the product should not be exposed to these temperatures for any extended period of time during the drying operation.

The particle size of the present flame retarding agents are such that substantially all of the particles will pass through a 325 mesh screen of the U5. standard screen series, which is equivalent to an average particle size of 44 microns.

An unexpected feature of the present flame retarding agents is the particularly high degree of activity obtained when the weight ratio of hydrated stannic oxide with respect to the other components, not including the halogen source, is about 1:4. Above or below this ratio the effectiveness of the combination as a flame retarding agent decreases significantly, as will be demonstrated in the accompanying examples. The reason for this phenomenon is not completely understood, however it appears that some enhanced degree of interaction among the various components of the flame retardant occurs when the combined weight of the other inorganic components, namely the colemanite, zinc oxide and magnesium oxide, is equal to about four times the weight of the hydrated stannic oxide.

One widely used method for determining the relative efficacy of various flame retarding agents is described in the American Society for Testing of Materials (ASTM) Test No. 1433-58. The test is performed by igniting a stream of butane gas eminiating from the aperture of a number 22 hypodermic needle. The tip of the resultant flame is placed within 0.5 inch of the test sample to be evaluated for flammability. The dimensions of the samples are 3 X 9 inches, and all exhibit the same average thickness. The sample to be tested is secured in a holder which together with the flame source is placed in an enclosure so as to minimize interfering air currents. A string is extended across the front of the sample and a second string is extended across the rear of the sample, the distance between the two strings being approximately 6 inches. The flame is then applied to the front edge of the sample, which is located 7 2 inches below the lower string. Samples wherein the flame burns through the lower string but is extinguished before reaching the upper string are designated as self-extinguishing. If the flame is extinguished before the lower string is burned the sample is designated non-buming. The length of the sample that burned was observed and recorded.

EXAMPLE 1 A polyvinyl chloride formulation of the following composition was prepared:

100 pans PVC 450 a vinyl chloride homopolymer manufactured by Diamond Shamrock Chemical Co. 40 parts Dioctylphthalate S pans Epoxidized soybean oil 2 parts Heat stabilizer containing compounds of barium and cadmium. as well known parts Stearic acid Flame Retardant As specified The formulation was blended on a heated 2-roll mill to form a homogeneous mixture. Test samples of the desired dimensions were obtained by pressing the resultant sheet to an average thickness of mils (0.015 inch) and cutting the sheet to obtain 3 by 9 inch sample. The samples were tested according to ASTM Test 1433-58 as described in the preceding specification. The length of sample burned prior to extinction of the flame was recorded and the results are summarized in Table 1. All parts are based on 100 parts by weight of polyvinyl chloride.

TABLE 1 compone nt.

EXAMPLE 2 This examples demonstrates the use of three mixtures containing zinc oxide and magnesium oxide as the second component of the present flame retardants for polyvinyl chloride. The samples were prepared and tested as described in the preceding specification. The values for flame spread (length of sample burned) given below represent the average obtained from 5 samples.

FLAME RETARDANT FLAME SPREAD COMPONENTS (phr) (inches) Hydrated stannic Oxide 1) 1.35

Zinc Oxide (1 Magnesium Oxide (3) Hydrated Stannic Oxide (l 1.35

Zinc Oxide (2) Magnesium Oxide (2) Hydrated Stannic Oxide 1 1.34

Zinc Oxide (3) Magnesium Oxide 1 Zinc Oxide (parts) Colemanite (parts) Hydrated Stannic Sample No. Oxide (parts) 1(control) 2(control) 3(control) 4(control) 5(control) 6(contro1) 7(control) 8( control) 9( control) 10(control) l 1 l2( control) 13(control) 14(control) 15(control) 16( control) 17 18 19 20(control) 21(control) 22(control) 23(contr0l) Sample No. 11, which exemplifies a composition of this invention, was significantly less flammable than samples 12, 13 or 14, all of which contained 1 phr of hydrated stannic oxide with various amounts of zinc oxide. Sample 11 burns less than sample 14, even though the latter contains 6 phr of the flame retardant but is not within the scope of the present invention.

Moreover, sample 17, which contains only 2.5 phr of flame retardant but exhibits a 1:4 weight ratio between the hydrated stannic oxide and zinc oxide, is equivalent in performance to sample 14.

inches of Sample Burned In addition to enhancing the flame retardancy imparted by the combination of hydrated stannic oxide and zinc oxide, magnesium oxide increases the resistance of polyvinyl chloride to heat induced degradatron.

EXAMPLE 3 This example demonstrates the efficacy of the present flame retardants in combination with a halogen 9 source as flame retardants for polyethylene. The formulation employed to prepare the test samples contained 100 parts of polyethylene (type NA 285, produced by US. Industries), 8 parts of a chlorinated l stannic oxide with either zinc oxide or colemanite, exhibits a limiting oxygen index of 20.5 or above indicating that the samples would burn only sluggishly in air, if at all.

, TABLE 2 SAMPLES 1 2 3 4 5 6 Hydrated Stannic Oxide (phr) 3 4 2 3 4 Colemanitet phr) 8 l2 l6 Zinc Oxide (phr) 8 l2 l6 L.O.l. value(average of two samples) I 20.5 20.7 20.4 21.4 21.9 21.4

paraffin containing 70 percent by weight of chlorine EXAMPLE 4 (Chlorowax' 70S produced by Diamond Shamrock Chemical Co., 8 parts of pentaerythritol as a heat stabilizer and a flame retardant as specified in the following Table 2. The polyethylene was blended with the additives using a two-roll mill heated to 110C. The resultant sheet was pressed to a thickness of A; inch and cut into test samples measuring 6 inches long by Vs inch wide. The flame retardancy of the various samples was determined using Limiting Oxygen lndex (L.O.l.) values.

The procedure for obtaining L.O.l. values is described in the November, 1966 issue of Modern Plastics TABLE 3 SAMPLES l 2 3 4 5 6 7 8 9 Hydrated Stannic v Oxide (phr) -2 3 4 5 2 3 4 5 O Colemanite( phr) 8 l2 1 6 2O m 0 Zinc Oxide(phr) 8 12 16 2O 0 L0]. value 22.8, 22.0 2L7 22.3 21.6 23.0 22.9 24.0 l8.8 (average of two samples) at pages 141-148 and 192. The test samples are placed 1 in a vertically oriented Pyrex glass tube, approximately EXAMPLE 5 3.5 inches in diameter, which has a bed of glass beads located at the bottom thereof and a smaller Pyrex glass tube of approximately 7 mm. in diameter located concentrically with respect to the larger tube. The samples are suspended above the smaller tube. A known mixture of oxygen and nitrogen is introduced at the bottom of the larger tube and flows up through theglass beads. The flow of each gas is controlled and monitored by means of valves and flow meters. i

The sample is ignited and the minimum concentration of oxygen required to support combustion is noted. The Limiting Oxygen Index is calculated using this minimum oxygen concentration and the formula wherein [0 and [N represent the relative amounts of oxygen and nitrogen, respectively, expressed in any convenient units such as flow rate in cubic centimeters per minute.

Samples with an oxygen index of 21.0 or less will burn readily in air while oxygen indeces increasingly greater than 21.0 indicate that the sample would burn with greater difficulty, if at all, in air. Polyethylene without any flame retardant has an oxygen index of 65 17.3 plus or minus 0.1. It will be noted from the following table that a polyethylene formulation containing one of the present two-component systems of hydrated This example demonstrates the flame retardancy imparted to polyurethane foams by the present combinations of hydrated stannic oxide with either zinc oxide or colemanite.

- The composition used to prepare the polymer contained parts by weight Poly G-435-DM (a polyfunctional polyoxy propylene polymer based on methyl glucoside andobtained from Olin Chemicals), Papi (polymethylene polyphenylisocyanate, manufactured by the Carwin Company) in the amount of 109 parts, 1.5 parts DC-l93(a dimethyl siloxysiloxane type surfactant by Dow Corning), 1 part dimethyl ethanol amine, 1 part dibutyltin dilaurate, 32 parts trichlorofluoromethane and 10 parts of a halogen source (either No. 23010, manufactured by Marbon Chemical Corp. and containing 68% chlorine or the Diels Alder adduct of hexachlorocyclopentadiene and 1,4 dichlorobutene). The foam was prepared by combining all of the ingredients except the isocyanate and mixing well. Thereafter, the isocyanate was added with additional mixing and the product poured into a container and allowed to rise. The foams were evaluated for flame retardancy as described in ASTM Test D-1692-67-T. Each of the samples containing the present flame retardants was rated self-extinguishing when tested according to this procedure. The test is performed by applying the flame of a Bunsen burner having a blue cone of about 1 /2 inches in height to the front edge of a ten foam samples measuring 6 inches by 2 inches by A inch 1 1 and allowing the flame to remain in contact with the sample for 60 seconds. The extent of burning is considered to be the furthest point reached by the flame front measured from the front edge, whereas the burning 12 2. The polymer composition of claim 1 wherein the polymer is polyvinyl chloride.

3. A polymer composition exhibiting enhanced flame retardancy wherein the polymer contains no halogen as rate in inches per minute is a measure of the time necan integral part thereof and is selected from the group essary for the flame to consume 5 inches of the foam consisting of polyolefins, acrylic polymers and polyuresample. A sample is judged non-burning if no evidence thanes, and wherein the polymer composition contains of ignition, which includes both a flame and a progresl) a flame retarding agent consisting of 20 percent, sive glow, is seen in each sample after removing the based on the weight of said flame retarding agent, of igniting flame. If the flame front of two or more specihydrated stannic oxide, the remaining 80 percent semens reaches the 5 inch mark the sample is judged lected from the group consisting of colemanite, zinc burning. A sample is judged self-extinguishing if the oxide and mixtures of zinc oxide and magnesium oxide length burned is less than 5 inches. The average extent and 2) between 1 and 12 times the weight of said flame of burning for the samples tested is summarized in the retarding agent of an organic halogen compound. following table, wherein all concentrations are ex- 4. The polymer composition of claim 3 wherein the pressed in parts by weight per 100 parts of the polyol organic halogen compound does not boil or decompose component (Poly G-435-DM) of the foam. at temperatures below 300C.

TABLE 4 l 2 3 4 5 6 Control FORMULATION PHR PHR PHR PHR PHR PHR PHR No. 23010 (halogen source) l0 10 10 Hydrated Stanic Oxide l0 2 10 2 Zinc Oxide 8 8 Diels Alder Adduct 10 10 10 (halogen source) Extent of Burning 6" 2" l" 2 6" l" 6" Average of ten specimens 5. The polymer composition of claim 4 wherein the organic halogen compound contains more than 20 The formulations which have incorporated therein percent by weight of said halogen. the combination of hydrated stannic oxide, zinc oxide 6. The polymer composition of claim 4 wherein said and one of the two alternative halogen sources yield a organic halogen compound is selected from the group self-extinguishing rating. In those instances when the consisting of halogenated aliphatic, cycloaliphatic and form contained only the No. 23010 halogen source, the v aromatic hydrocarbons. samples were rated as burning. The samples containing 7. The polymer composition of claim 4 wherein the the No. 23010 halogen source and hydrated stannic halogen is chlorine. oxide exhibited an average burned length of 2 inches, 8. The polymer composition of claim 3 wherein the whereas a similar composition containing zinc oxide organic halogen compound is a chlorinated paraffin burned for only 1 inch. wax or a chlorinated bicyclic hydrocarbon.

What is claimed is: 9. A composition for imparting flame retardancy to a l. A polymer composition exhibiting enhanced flame material selected from the group consisting of a) haloretardancy, wherein the polymer is selected from the gen-containing synthetic organic polymers and b) nongroup consisting of polyvinyl chloride, polyvinylidene halogen-containing organic polymers in combination chloride and copolymers of vinyl chloride and vinyliwith an organic halogen source, said composition condene chloride with one another and with ethylenically sisting essentially of hydrated stannic oxide and a secunsaturated monomers, wherein said polymer composiond component selected from the group consisting of tion contains between 0.5 and 10 parts by weight per colemanite, zinc oxide and mixtures of zinc oxide and 100 parts of said polymer of a flame retardant containmagnesium oxide wherein the weight ratio of zinc oxide ing 20 percent by weight of hydrated stannic oxide and to magnesium oxide is between 1:3 and 3:1, respec- 80 percent by weight of a second component selected tively, and the weight ratio of hydrated stannic oxide to from the group consisting of colemanite, zinc oxide and said second component is 1:4, respectively. mixtures of zinc oxide and magnesium oxide. 

1. A POLYMER COMPOSITION EXHIBITING ENHANCED FLAME RETARDANCY, WHEREIN THE POLYMER IS SELECTED FROM THE GROUP CONSISTING OF POLYVINYL CHLORIDE, POLYVINYLIDENE CHLORIDE AND COPOLYMERS OF VINYL CHLORIDE AND VINYLIDENE CHLORIDE WITH ONE ANOTHER AND WITH ETHYLENICALLY UNSATURATED MONOMERS, WHEREIN SAID POLYMER COMPOSITION CONTAINS BETWEEN 0.5 AND 10 PARTS BY WEIGHT PER 100 PARTS OF SAID POLYMER OF A FLAME RETARDANT CONTAINING 20 PERCENT BY EIGHT OF HYDRATED STANNIC OXIDE AND 80 PERCENT BY WEIGHT OF A SECOND COMPONENT SELECTED FROM THE GROUP CONSISTING OF COLEMANITE, ZINC OXIDE AND MIXTURES OF ZINC OXIDE AND MAGNESIUM OXIDE.
 2. The polymer composition of claim 1 wherein the polymer is polyvinyl chloride.
 3. A polymer composition exhibiting enhanced flame retardancy wherein the polymer contains no halogen as an integral part thereof and is selected from the group consisting of polyolefins, acrylic polymers and polyurethanes, and wherein the polymer composition contains 1) a flame retarding agent consisting of 20 percent, based on the weight of said flame retarding agent, of hydrated stannic oxide, the remaining 80 percent selected from the group consisting of colemanite, zinc oxide and mixtures of zinc oxide and magnesium oxide and 2) between 1 and 12 times the weight of said flame retarding agent of an organic halogen compound.
 4. The polymer composition of claim 3 wherein the organic halogen compound does not boil or decompose at temperatures below 300*C.
 5. The polymer composition of claim 4 wherein the organic halogen compound contains more than 20 percent by weight of said halogen.
 6. The polymer composition of claim 4 wherein said organic halogen compound is selected from the group consisting of halogenated aliphatic, cycloaliphatic and aromatic hydrocarbons.
 7. The polymer composition of claim 4 wherein the halogen is chlorine.
 8. The polymer composition of claim 3 wherein the organic halogen compound is a chlorinated paraffin wax or a chlorinated bicyclic hydrocarbon.
 9. A composition for imparting flame retardancy to a material selected from the group consisting of a) halogen-containing synthetic organic polymers and b) non-halogen-containing organic polymers in combination with an organic halogen source, said composition consisting essentially of hydrated stannic oxide and a second component selected from the group consisting of colemanite, zinc oxide and mixtures of zinc oxide and magnesium oxide wherein the weight ratio of zinc oxide to magnesium oxide is between 1:3 and 3:1, respectively, and the weight ratio of hydrated stannic oxide to said second component is 1:4, respectively. 